This invention relates to milling and molding apparatus and particularly to such apparatus in which blanks of molding stock are stamped from a continuously moving ribbon of moldable material taken from a plasticizing mill and returned to the mill after stamping.
In molding machines such as disclosed in the Gora U.S. Pat. Nos. 2,548,305, 2,745,135, and 2,952,035, moldable material is taken from a plasticizing mill in the form of a continuous ribbon and passed through a stamping section of the molding machine. Blanks of molding stock are then stamped from the ribbon and inserted in bottle caps or the like for subsequent molding therein. The remaining part of the ribbon continues through the stamping section and is returned to the plasticizing mill as mill stock. The milling and molding operations are continuous with fresh mill stock being added to supplement the returned ribbon. In those prior milling and molding apparatus, the ribbon of moldable material is drawn from the plasticizing mill and through the stamping section by pinch rollers positioned along the return path of the ribbon to the mill.
In the above systems, the ribbon is of uncured rubber and is subject to shrinkage and breakage. With breakage, the plasticizing mill continues to output ribbon which must be manually threaded through the system, including stamping section, until it is again gripped by the pinch rollers. This requires the operator to handle the ribbon near the stamping section where injury to the operator from the stamping die is a likely result.
An object of this invention is to provide a self-threading ribbon feed for feeding a ribbon of moldable material from a plasticizing mill through a stamping section of a molding machine, and for returning the ribbon to the mill.
A further object of this invention is to provide a ribbon feeding system wherein the stretching of the ribbon is reduced and which provides for ease in tracking the speed of the mill with compensation for stretching and shrinkage which does result.
In prior milling and molding machines the plasticizing mill operates continuously even when the molding machine is shut down. As a result, when the molding machine is shut down, it is customary to cut the ribbon and feed it manually back to the mill in order to bypass the molding machine. Such cutting and manual feeding of the ribbon is not only an inconvenience; it makes poor use of the operator's time and, with rethreading, presents a danger to the operator. There is also the risk of overloading the mill with manual return of the cut ribbon.
It is thus a further object of this invention to provide a system for feeding ribbon through a stamping section which will operate continuously even when the molding machine is shut down.
In prior milling and molding apparatus it is also difficult to regulate the bite of moldable material taken from the ribbon for each blank of molding stock.
A further object of this invention is to provide a precision mold bite control capable of reproducible initial settings.